An Ultrafast Nonvolatile Memory with Low Operation Voltage for High-Speed and Low-Power Applications

Memory plays a vital role in modern information society. High-speed and low-power nonvolatile memory is urgently demanded in the era of big data. However, ultrafast nonvolatile memory with nanosecond-timescale operation speed and long-term retention is still unavailable. Herein, an ultrafast nonvolatile memory based on van der Waals heterostructure is proposed, where a charge-trapping material, graphdiyne (GDY), serves as the charge-trapping layer. With the band-engineered heterostructure and excellent charge-trapping capability of GDY, charges are directly injected into the GDY layer and are persistently captured by the trapping sites in GDY, which result in an ultrafast writing speed (8 ns), a low operation voltage (30 mV), and a long retention time (over 10⁴ s). Moreover, a high on/off ratio of 10⁶ is demonstrated by this memory, which enables the achievement of multibit storage with 6 discrete storage levels. This device fills the blank of ultrafast nonvolatile memory technology, which makes it a promising candidate for next-generation high-speed and low-power-consumption nonvolatile memory.     

Investigation of charge-trap memories with AlN based band engineered storage layers

This paper presents the investigation of the electrical properties of charge-trap memories with AlN based storage layers. The memory performance and reliability are studied in details and compared with the ones of a reference device using standard Si₃N₄ as storage layer. An engineered charge trapping layer is also proposed, made by an AlN/Si₃N₄ double layer, which shows reduced program/erase voltages, combined with 10⁶ excellent endurance and good retention (ΔV_T > 5 V after 10 years at 125 °C).     

氮化硅和氮氧化硅在俄歇电子谱分析中的电子束和离子束辐照效应

本文观察和测量了Si_3N_4和SiO_xN_y薄膜在俄歇电子谱(AES)分析中的电子束和离子束效应。结果表明在高束流密度电子束辐照下没有观察到任何损伤特征峰。延长辐照时间仅导致氧的解吸和Si、N讯号增加,最后达到一个稳定态。Si_3N_4和SiO_xN_y对离子辐照很容易造成损伤。但在高束流密度的电子束辐照下离子损伤的表面可以恢复。恢复程度与电子束流密度、束能、辐照时间和样品制备工艺有关。最后,本文对离子辐照损伤和恢复的机理进行了讨论。     

High temperature annealing of mnos devices and its effect on si-nitride stress,interface charge density and memory properties

The effects of high temperature annealing in N₂ and H₂ ambients upon the following properties of MNOS devices have been investigated: Si-nitride stress, etch rate, index of refraction, fixed interface charge and fast surface state density, memory window and charge retention at elevated temperatures. The CVD Si-nitride and Si-oxynitride films were deposited at temperatures as low as 610°C with a NH₃/SiH₄ ratio of 1000:1, the heat treatments were performed in the temperature range from 640°C to 1130°C. A similar N₂-annealing behavior was found for film stress and flatband voltage. The film stress increased with increasing annealing time and temperature while the interface charge density changed from high positive values (Q_N/q = 4 × 10¹²cm⁻2) after nitride deposition at 610°C to high negative values (Q_N/q = -4 × 10¹²cm⁻2) after annealing at 930°C, The fast interface state density increased while the charge retention time was drastically reduced. The changes of the properties by N₂ annealing are mainly attributed to decomposition of SiH and NH bonds. Minor effects were obtained by annealing in H₂ and the drastic changes caused by N₂ annealing could be reversed to a great extent by subsequent H₂ annealing. Finally the different effects of deposition and annealing temperature on the propertiesare discussed .     

Effective Prevention of Charge Trapping in Graphitic Carbon Nitride with Nanosized Red Phosphorus Modification for Superior Photo(electro)catalysis

The high occurrence of trapped unreactive charges due to chemical defects seriously affects the performance of g‐C₃N₄ in photocatalytic applications. This problem can be overcome by introducing ultrasmall red phosphorus (red P) crystals on g‐C₃N₄ sheets. The elemental red P atoms reduce the number of defects in the g‐C₃N₄ structure by forming new chemical bonds for much more effective charge separation. The product shows significantly enhanced photocatalytic activity toward hydrogen production. To the best of our knowledge, the hydrogen evolution rate obtained on this hybrid should be the highest among all P‐containing g‐C₃N₄ photocatalysts reported so far. The trapping and detrapping processes in this red P/g‐C₃N₄ system are thoroughly revealed by using time‐resolved transient absorption spectroscopy.     

基于Si3N4的电荷俘获型存储器中氧缺陷的第一性原理研究

Based on first principle calculations, a comprehensive study of substitutional oxygen defects in hexagonal silicon nitride （β-Si3N4） has been carried out. Firstly, it is found that substitutional oxygen is most likely to form clusters at three sites in Si3N4 due to the intense attractive interaction between oxygen defects. Then, by using three analytical tools （trap energy, modified Bader analysis and charge density difference）, we discuss the trap abilities of the three clusters. The result shows that each kind of cluster at the three specific sites presents very different abilities to trap charge carriers （electrons or holes）： two of the three clusters can trap both kinds of charge carriers, confirming their amphoteric property; While the last remaining one is only able to trap hole carriers. Moreover, our studies reveal that the three clusters differ from each other in terms of endurance during the program/erase progress. Taking full account of capturing properties for the three oxygen clusters, including trap ability and endurance, we deem holes rather than electrons to be optimal to act as operational charge carriers for the oxygen defects in Si3N4-based charge trapping memories.     

Analysis on Conductivity of nc—Si：H Films

A conduction channel model is propsed to explain the high conductivity property of nc-Si:H.Detailed energy band diagram is developed based on the analysis and calculation ,and the conductivity of the nc-Si:H was then analysed on the basis of energy band theory.It is assumed that the conductivity of the nc-Si:H stems from two parts:the conductance of the interface,where the transport mechanism is identified as a thermal -assisted tunneling process,and the conductance along the channel around the grain,which mainly determined the high conductivity of the nc-Si:H.The conductivity of nc-Si:H is calculated and compared with the experiment data .The theory is in agreement with the experiment.     

Low-temperature deposition of silicon oxide and silicon nitride by reactive magnetron sputtering

In this study, oxide and nitride films were deposited at room temperature through the reaction of silicon sputtered by argon and oxygen ions or argon and nitrogen ions at 250 and 350 W with 0.67 Pa pressure. It was observed that for both thin films the deposition rates increase with the applied RF power and decrease with the increase of the gas concentration. The Si/O and Si/N ratio were obtained through RBS analyses and for silicon oxide the values changed from 0.42 to 0.57 and for silicon nitride the values changed from 0.4 to 1.03. The dielectric constants were calculated through capacitance-voltage curves with the silicon oxide values varying from 2.4 to 5.5, and silicon nitride values varying from 6.2 to 6.7, which are good options for microelectronic dielectrics.     

MOS Capacitance-Voltage Characteristics:Ⅳ.Trapping Capacitance from 3-Charge-State Impurities

正Metal-Oxide-Semiconductor Capacitance-Voltage(MOSCV) characteristics containing giant carrier trapping capacitances from 3-charge-state or 2-energy-level impurities are presented for not-doped,n-doped,pdoped and compensated silicon containing the double-donor sulfur and iron,the double-acceptor zinc,and the amphoteric or one-donor and one-acceptor gold and silver impurities.These impurities provide giant trapping capacitances at trapping energies from 200 to 800 meV(50 to 200 THz and 6 to 1.5μm),which suggest potential sub-millimeter,far-infrared and spin electronics applications.     

高导热氮化硅陶瓷的快速制备和性能控制

氮化硅陶瓷力学性能优异,理论热导率高,是大功率电力电子器件的关键热管理材料。但是,高导热氮化硅陶瓷烧结温度高、保温时间长,因此制备成本居高不下,对于产业化应用不利。本研究提出了一种快速制备高导热氮化硅陶瓷的方案。以Y2O3-MgO-C作为烧结助剂,以高纯硅粉作为起始原料,通过流延成型和硅粉氮化制备素坯,在1900℃、0.6MPa保温2h制备出高导热氮化硅陶瓷。研究了C的添加量对于氮化硅陶瓷的致密化、晶相、微结构、力学性能以及热导率的影响规律。最终制备的氮化硅陶瓷密度可以达到99%以上,热导率达到98W/m·K。     

聚苯胺光学吸收及应用

从结构和性能的角度对聚苯胺不同形态因电子或极子跃迁引起的在可见近红外区的吸收特性进行了总结。重点讨论了本征态盐的分子链构像结构对光学吸收的影响，报道了作者在降苯胺用于透明导电材料和节能方面的一些设想和研究结果。     

Understanding Temperature‐Dependent Charge Extraction and Trapping in Perovskite Solar Cells

Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)‐dependent studies. Based on p‐i‐n type PSCs with prototype methylammonium lead triiodide (MAPbI₃) perovskite absorbers, T‐dependent photovoltaic properties are explored and negative T‐coefficients for the three device parameters (V_OC, J_SC, and FF) are observed within a wide low T‐range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T‐behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T‐dependent device behaviors based on MAPbI₃ devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T‐dependencies of J_SC and FF, which eventually leads to nearly T‐invariable PCEs. These results indicate that charge extraction with the utilized all‐organic charge transporting layers is not a limiting factor for low‐T device operation, meanwhile the trap passivation layer of choice can play a role in the T‐dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature‐variable environment.     

Effect of deposition conditions on charging processes in SiNx: Application to RF-MEMS capacitive switches

The paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The dielectric charging is investigated with the aid of Metal-Insulator-Metal (MIM) capacitors with different thickness dielectric film and symmetric and asymmetric metal contacts. The experimental results demonstrate that the charging process is almost symmetric in low temperature deposited silicon nitride. Experiments performed in both MIM and MEMS reveal that the charging process is strongly affected by temperature. Specifically at high temperatures the charging rate increases exponentially with temperature.     

Frequency and temperature dependent dielectric properties of Al/Si3N4/p-Si(1 0 0) MIS structure

The dielectric properties of Al/Si₃N₄/p-Si(1 0 0) MIS structure were studied from the C-V and G-V measurements in the frequency range of 1 kHz to 1 MHz and temperature range of 80-300 K. Experimental results shows that the ε′ and ε″ are found to decrease with increasing frequency while the value of ε′ and ε″ increase with increasing temperature, especially, above 160 K. As typical values, the dielectric constant ε′ and dielectric loss ε″ have the values of 7.49, 1.03 at 1 kHz, and only 0.9, 0.02 at 1 MHz, respectively. The ac electrical conductivity (σ_ac) increases with both increasing frequency and temperature. The activation energy of 24 meV was calculated from Arrhenius plot at 1 MHz. The results indicate that the interfacial polarization can be more easily occurred at low frequencies and high temperatures.     

High-voltage SiC and GaN power devices

The recent progress in the development of high-voltage SiC and GaN power switching devices is reviewed. The experimental performance of various rectifiers and transistors, which have been demonstrated, is discussed. Material and processing challenges and reliability concerns on SiC and GaN power devices are also described. The future trends in device development and commercialization are pointed out.     

Supramolecular Chemistry in Molten Sulfur: Preorganization Effects Leading to Marked Enhancement of Carbon Nitride Photoelectrochemistry

Here, a new method for enhancing the photoelectrochemical properties of carbon nitride thin films by in situ supramolecular‐driven preorganization of phenyl‐contained monomers in molten sulfur is reported. A detailed analysis of the chemical and photophysical properties suggests that the molten sulfur can texture the growth and induce more effective integration of phenyl groups into the carbon nitride electrodes, resulting in extended light absorption alongside with improved conductivity and better charge transfer. Furthermore, photophysical measurements indicate the formation of sub‐bands in the optical bandgap which is beneficial for exciton splitting. Moreover, the new bands can mediate hole transfer to the electrolyte, thus improving the photooxidation activity. The utilization of high temperature solvent as the polymerization medium opens new opportunities for the significant improvement of carbon nitride films toward an efficient photoactive material for various applications.     

Plasmonic Charge Transfers in Large-Scale Metallic and Colloidal Photonic Crystal Slabs

The challenges in plasmonic charge transfer on a large-scale and low losses are systematically investigated by optical designs using 1D-plasmonic lattice structures. These plasmonic lattices are used as couplers to guide the energy in an underneath sub-wavelength titanium dioxide layer, resulting in the photonic crystal slabs. So far, photodetection is possible at energy levels close to the semiconductor bandgap; however, with the observed hybrid plasmonic–photonic modes, other wavelengths over the broad solar spectrum can be easily accessed for energy harvesting. The photo-enhanced current is measured locally with simple two-point contact on the centimeter-squared nanostructure by applying a bias voltage. As lattice couplers, interference lithographically fabricated conventional gold grating provides an advantage in fabrication; this optical concept is extended for the first time toward colloidal self-assembled nanoparticle chains to make the charge injection accessible for large-scale at reasonable costs with possibilities of photodetection by electric field vectors both along and perpendicular to the grating lines. To discuss the bottleneck of unavoidable isolating ligand shell of nanoparticles in contrast to the directly contacted nanobars, polarization-dependent ultrafast characterizations are carried out to study the charge injection processes in femtosecond resolution.     

The Opportunity of Negative Capacitance Behavior in Flash Memory for High-Density and Energy-Efficient In-Memory Computing Applications

Flash memory is a promising candidate for use in in-memory computing (IMC) owing to its multistate operations, high on/off ratio, non-volatility, and the maturity of device technologies. However, its high operation voltage, slow operation speed, and string array structure severely degrade the energy efficiency of IMC. To address these challenges, a novel negative capacitance-flash (NC-flash) memory-based IMC architecture is proposed. To stabilize and utilize the negative capacitance (NC) effect, a HfO₂-based reversible single-domain ferroelectric (RSFE) layer is developed by coupling the flexoelectric and surface effects, which generates a large internal field and surface polarization pinning. Furthermore, NC-flash memory is demonstrated for the first time by introducing a RSFE and dielectric heterostructure layer in which the NC effect is stabilized as a blocking layer. Consequently, an energy-efficient and high-throughput IMC is successfully demonstrated using an AND flash-like cell arrangement and source-follower/charge-sharing vector-matrix multiplication operation on a high-performance NC-flash memory.